The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystals orientation control layer for orientating liquid crystal uniformly, a method and apparatus for manufacturing the same, and a method for manufacturing a mask for use in the manufacturing apparatus.
In the operation of a liquid crystal display device, the liquid crystal material should be orientated as desired. Thus, it is imperative to control the orientation of the liquid crystal, which is accomplished by a liquid crystal orientation control layer (to be called hereinafter an "orientation layer"). The mechanism by which liquid crystal is orientated is not yet known exactly, but empirically, there have been known methods for depositing a silicon oxide layer on a substrate with a tilt or for forming the grated surface of a substrate. Particularly, in 1911, it was discovered that when a glass surface is rubbed with paper in a predetermined direction, the long axes of the liquid crystal molecules are orientated along the rubbing direction. Since then, a method for rubbing an organic layer made of a polyimide or the like has been widely used, thereby allowing mass-production of liquid crystal display devices.
FIG. 1 is a cross-sectional view of a conventional orientation layer and shows that a polyimide orientation layer 2 having a uniformly grooved surface is formed on a substrate 1 such that liquid crystal molecules 3 are orientated in a predetermined direction. In this method, an orientation layer made of polymer or organic material is deposited on the substrate 1 and then the surface thereof is rubbed in a predetermined direction with cotton or a cloth, which is advantageous in view of production of large layers and uniform layers. Thus, this method is more widely used than the method for depositing silicon oxide layer with a tilt.
As shown in FIG. 2, a rotary roller 5 with a cloth 4 (e.g., nylon or rayon) fixed on the surface thereof is rolled over the substrate 1 on which the polyimide orientation layer 2 is coated, with a constant power, thereby forming grooves.
However, such an orientation layer forming method by the rubbing treatment is liable to generate static electricity due to the friction produced when the rotary roller 5 rotates while in close contact with the surface of the substrate 1. Thus, if a thin-film transistor or similar device which is sensitive to the static electricity is disposed beneath the polyimide orientation layer 2, the device is easily damaged.
Currently, in order to solve this problem, there is a method for neutralizing the static electricity by supplying ionized air having the opposite polarity with respect to the rotary roller. However, since the air cannot be supplied in amounts sufficient to counteract the high voltages which are instantaneously generated, the production of inferior devices is unavoidable.
Also, there is a disadvantage in that the grooves are not formed uniformly. Since grooves having a severe tilt are difficult to form by rubbing, it is difficult to increase a liquid crystal pre-tilt angle. Specifically, the pre-tilt angle is an important factor for determining picture quality. Therefore, it is essential to regulate the pre-tilt angle.